In this article, the author analyses recent Korean Supreme Court decisions about antitrust cases. The Court ruled that the presumption clause in the Monopoly Regulation and Fair Trade Act is for the legal presumption but not for the factual presumption. The Court noteworthily declared that price leadership, if substantiated, may rebut presumption of agreement. The author criticizes the Court``s opinion that actual reduction of competition is prerequisite for the presumption of agreenment. Such aruling would make the presumption clause ineffective.